1. Make sure your boots fit and are broken in properly
Of all the various blister prevention tips published in this article and elsewhere, I think this one (substituting "shoes" for "boots" where appropriate) is by far the most important and helpful.
I was fortunate enough to walk the entire way from SJPP to Fisterra this past May and June with only one blister - and that was a pinch blister that formed on the side of my heel after I tried swapping out the inserts I had started walking in for a (different) backup pair I had bought along with me.
Otherwise, breaking in my shoes well in advance of starting out and staying with a simple tried-and-true foot wardrobe/regimen (= lightweight Darn Tough socks with neither petroleum jelly, foot powder, nor liners) served me well. Meanwhile, nearly early everyone I talked to who was suffering through blisters were wearing shoes and/or socks they had bought shortly before starting their walk or had not trail-tested/broken in sufficiently.
I'm sure there are plenty of cases of folks coming down with blisters even with footwear that hadn't caused problems in the past. But for the most part, I still think it's one of those things where an ounce of prevention (or in this case, several weeks/months of pre-Camino walking) really is worth a pound of cure.